Mangrove Status & Restoration
Mangroves of the Niger Delta: Their Importance, Threats, and Possible Restoration Elijah I. Ohimain1
INTRODUCTION angroves are among the most important ecosystems in the world. Mangroves has social, economic and ecological functions, hence are true agents of sustainable development. Mangroves are made up a unique group of trees and shrubs that grow in the intertidal zones of tropical and subtropical estuaries, creeks and sheltered bay across the world (Osborne and Berjak 1997; Ukpong 2000). Mangroves ecosystems are found approximately between 30°N and 30°S (Gilbert and Janssen 1998). They are variously described as coastal woodland, tidal forest and are still regarded as wastelands in some uninformed communities. Mangrove trees can grow up to 40 meters high or as shrubs below the high-water level of spring tides (Corcoran et al. 2007). Blasco et al. (1996) refers to mangrove as ecological term referring to the taxonomically diverse assemblages of trees and shrubs that form the dominant plant communities in tidal, saline wetlands along sheltered tropical and subtropical coasts. Tomlinson (1986) include the taxonomically diverse group of species that are restricted to and do play a major role in the intertidal environment as ‛true’ mangroves. Mangrove species exhibit a range of adaptations for coping with flooding, anaerobic conditions and high salinities, which fluctuates daily and seasonally depending on tidal movement. The term mangrove has been used in a broad sense to include species that are restricted to and those that occur in, but not necessarily restricted to the intertidal environment. Due to the dynamic nature of the swamp landscape, several physiographic habitats have evolved within mangrove ecosystems. Habitat differences relate to several factors including swamp gradient, hydrology and topography, salinity, substrate texture and carbonate content of the soil (Ukpong 1997). Mangrove is an ecosystem complex consisting not just mangrove vegetation, but also mangrove soils, brackish water, fisheries, wildlife and even microbes. Human populations live in and around mangrove ecosystems forming part of the complex because of their activities such as resources extraction that affect the
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1. Email: eohimain@yahoo.com; Biodiversity Conservation and Research Group, Biological Sciences Department, Faculty of Science, Niger Delta University, Wilberforce Island, Bayelsa State, Nigeria.
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survival of mangroves, both existing stands and newly revegetated mangroves (Walter 1997). Anthropogenic activities in the current century are fast impacting on mangrove ecosystems globally. Despite the importance of mangroves, the ecosystem is under threat due to human exploitation. The unsustainable exploitation of mangrove trees for fuel wood has led to the destruction of mangrove ecosystems globally. Mangroves are also destroyed by expanding coastal cities with mangrove ecosystems filled with sand for construction purposes. Sewage, solid wastes and other kinds of wastes including non-biodegradable plastics are freely dumped into mangrove forests. The exploitation of petroleum resources located in mangrove ecosystems has impacted the ecosystems. Oil exploration activities that impact on mangroves include dredging, seismic exploration, pipeline construction, and well drilling. In addition, oil spills arising from oil production and transportation have detrimental effects on mangroves. Due to the activities of illegal bunkering, oil spills are becoming a regular occurrence in the Niger Delta. The impacts on mangrove from multiple sources are now overwhelming the ecosystem and starting to threaten the ecological functions and integrity of the wetlands. For instance, the role of mangroves in the control of coastal erosion, which is now more relevant owing to the observed climate change, is threatened. Hence, the aim of this paper is therefore to present the importance of mangroves, threats facing mangroves and possibility of mangrove restoration. MANGROVE ECOSYSTEM OF NIGERIA The size of mangrove ecosystem in the World was estimated as 150,000 – 182, 000 km2 (Spalding et al. 1997; Lewis 2001; Blasco et al. 1996; Dodd et al. 1998). Nigeria has the largest mangrove stand in Africa and the third largest in the world after India and Indonesia (Corcoran et al. 2007). The authors estimated the current size of Nigerian mangrove to be 7,386km2 having lost 26% since 1980. While many authors estimated the size of mangrove ecosystem in Nigeria as 10,000 km2 (Jackson and Lewis 2000; Lewis and Jackson 2000), but Spalding et al. (1997) in the Mangrove Atlas of the World estimated 11,134 km2 of mangrove in Nigeria. Estimates by Wilkie and Fortuna (2003) also show
